The sorption behaviour and separation of some metal thiocyanate complexes on polyether-based polyurethane foam

The preliminary screening tests on the preconcentration of lanthanum(III), aluminium(III), molybdenum(VI), gallium(III) and tungsten(VI) thiocyanate complexes in aqueous media by unloaded foam indicated a reasonable percentage of metal ions were retained on the foam. The influence of various parameters affecting the retention of these complex species from the aqueous media by the foam were critically studied and the possible mechanisms of the sorption of the compounds were suggested. However, owing to the complex chemical nature of the polyether-polyurethane foam, several mechanisms may be involved simultaneously. Attempts for the quantitative retention and recovery of the tested complexes by the foam columns were also made and satisfactory results were obtained. The height equivalent to theoretical plates (HETP) of the foam columns were calculated from the chromatograms and break through capacity curve and were found in the range 1.8-2.3 mm at flow rates up to 15 cm(3)/min. The proposed foam column method has been successfully used for the separation of a series of complex mixtures of the tested metal thiocyanate complexes in aqueous media. The membrane properties of the foam sorbents offer unique advantages over conventional bulk type granular sorbents in rapid, versatile effective separations and preconcentrations of different complexes from fluid samples.     

Chemical recycling of polyurethanes and separation of the components by supercritical ammonia

Chemical recycling of a polyurethane elastomer and a flexible foam based on methylenebis(phenyl isocyanate) (MDI) and a polyetherpolyol was performed by ammonolytic cleavage of urethane and urea bonds under supercritical conditions. Resulting products were the polyols, the amines corresponding to the isocyanates used, and unsubstituted urea. Under suitable conditions the polyetherpolyol was completely separated from the other ammonolysis products which in turn can be further separated and used for the manufacture of polyurethanes or for the synthesis of diisocyanates.     

Liquid foam as a template for the synthesis of iron oxyhydroxide nanoparticles

Liquid foams have been used as a template to prepare iron oxyhydroxide nanoparticles. This is achieved by a process of electrostatic entrapment of Fe2+/Fe3+ ions in the foam stabilized by the surfactant sodium dodecyl sulfate followed by the in situ hydrolysis of the metal ions. Infrared and selected area electron diffraction measurements suggest the formation of a mixture of beta-FeO(OH) and gamma-FeO(OH) crystallographic phases after the in situ hydrolysis of the metal ions in the foam template. Transmission electron microscopy analysis of the powders obtained from the foam indicates that the particles are fairly monodisperse with an average size of around 50 nm. Scanning electron microscopy pictures reveal that the particles form loosely bound aggregates of around 300 nm. After the powders obtained in the foam are annealed at 400 degrees C, X-ray diffraction measurements show that the FeO(OH) particles are converted to alpha-Fe2O3. The mechanistic aspects of metal ion hydrolysis in a foam are discussed, and some of the advantages of this method vis-à-vis the normal solution-based methods are outlined.     

Urethane-hydrolyzing enzyme from Citrobacter sp

Urethane, a cancer-causing chemical, was reported to contaminate alcoholic beverages such as whisky, liquor, wine and sake. Enzymatic removal of urethane would be a possible approach to remove this potentially hazardous chemical from alcoholic beverages. We found that Citrobacter sp. isolated from mouse feces stoichiometrically decomposed urethane to ethanol and ammonia. We named this enzyme "urethanase." Partially purified urethanase could hydrolyze several carbamates and some amides. However, urea, N-alkyl ureas and ethyl esters of organic acids were not hydrolyzed at all. These results suggest that urethanase belongs to the category of amidase. The enzyme was inactive in high concentrations of alcohol and at acidic pH and was practically ineffective for the elimination of urethane from alcoholic beverages.     

Purification and Characterization of a Urethanase from Penicillium variabile

Urethanase produced by Penicillium variabile was purified through ultrasonication, concentration by polyethylene glycol 20,000, and Superdex G-200 gel filtration chromatography. The molecular weight of urethanase was determined to be around 96 kDa by gel filtration. The purified enzyme showed a single band in SDS-PAGE with the molecular weight of ~13.7 kDa, which suggests that the enzyme has a multimeric structure composed of the same subunits. Peptide map fingerprinting analysis was then carried out by MALDI/TOF-TOF MS. Within the known sequences in NCBI, glucosamine-6-phosphate deaminase and 6-phosphogluconate dehydrogenase get high score as compared with urethanase. Sequence analysis informs that N-terminal sequence of urethanase is GTNTADNDAA. The Minchaelis constant (K _m) and maximum reaction rate (V _m) of urethanase are 27.2 mmol/L and 156.25 μmol/L min, respectively.     

Effect of limited hydrolysis on the interfacial rheology and foaming properties of beta-lactoglobulin A

Hydrolysis of beta-lactoglobulin (beta-Lg), genetic variant A, using a serine protease specific for glutamic and aspartic acid residues from Bacillus licheniformis (BLP), resulted in improved foam overrun and foam stability. Limited hydrolysis (19-26% hydrolysed beta-Lg) led to a more rapid increase in the viscoelastic properties of air/water interfacial films and a concomitant increase in foam overrun compared with intact beta-Lg, presumably due to increased exposure of hydrophobic areas. The increased exposure did not, however, cause formation of an interfacial layer with increased viscoelastic properties. More extended hydrolysis (86% hydrolysed beta-Lg) resulted in a higher initial overrun than the unhydrolysed sample and the best foam stability. The interfacial elasticity and viscosity, though, was the lowest observed. Thus, high maximum values of these interfacial properties are not necessary prerequisites for formation of a voluminous and stable foam.     

Mechanical Activation Drastically Accelerates Amide Bond Hydrolysis,Matching Enzyme Activity

Amide bonds, which include peptide bonds connecting amino acids in proteins and polypeptides, give proteins and synthetic polyamides their enormous strength. Although proteins and polyamides sustain mechanical force in nature and technology, how forces affect amide and peptide bond stability is still unknown. Using single‐molecule force spectroscopy, we discover that forces of only a few hundred pN accelerate amide hydrolysis 10⁹‐fold, an acceleration hitherto only known from proteolytic enzymes. The drastic acceleration at low force precedes a moderate additional acceleration at nN forces. Quantum mechanochemical ab initio calculations explain these experimental results mechanistically and kinetically. Our findings reveal that, in contrast to previous belief, amide stability is strongly force dependent. These calculations provide a fundamental understanding of the role of mechanical activation in amide hydrolysis and point the way to potential applications from the recycling of macromolecular waste to the design of bioengineered proteolytic enzymes.     

Isolation and Characterization of Urethanase from Penicillium variabile and Its Application to Reduce Ethyl Carbamate Contamination in Chinese Rice Wine

A strain with urethanase activity was isolated from mouse gastrointestine. By combination of morphological characterization of the colony, hyphae, and spore and the sequence analysis of its rDNA ITS, the strain was determined as Penicillium variabile and named as P. variabile JN-A525. The enzymatic properties of urethanase from P. variabile JN-A525 were further studied. The optimum temperature and pH value of urethanase are of 50 °C and 6.0, respectively. The enzyme maintains stability when the temperature is below 50 °C and the pH is in the range of 7.0–10.0. The enzyme also exhibits ethanol tolerance. It can remove ethyl carbamate from Chinese rice wine without the change of flavor substances in the wine.     

A new concept for recycling of thermosetting resins I: The case of crosslinkable copolyesters

A new approach for the recycling and the direct reuse of thermosetting resins has been successfully applied to a crosslinkable copolyester system. The process is essentially an acetolysis of the polymeric network leading to multifunctional oligomers with carboxy and acetoxy end groups. These species can react again upon heating to give a new crosslinked copolyester system. In this work, the parameters for the acetolysis process have been established and the products obtained have been compared to the starting ones, by differential scanning calorimetry, thermogravimetric analysis, mass spectrometry and dynamic mechanical analysis. The hydrolysis of the crosslinked copolyester has also been studied as a variation of recycling resulting in recovery of the monomeric units which compose the network.     

Probing potential medium effects on phosphate ester bonds using 18O isotope shifts on 31P NMR

Dipolar aprotic cosolvents, such as DMSO and acetonitrile, accelerate the rates of hydrolysis of phosphate monoester dianions. It has been speculated that the rate acceleration arises from the disruption of hydrogen bonding to the phosphoryl group. An aqueous solvation shell can stabilize the dianionic phosphoryl group by forming hydrogen bonds to the phosphoryl oxygens, whereas solvents such as DMSO are incapable of forming such bonds. It has been proposed that the loss of stabilization could result in a weakened P-OR ester bond, contributing to the observed faster rate of hydrolysis. Computational results support this notion. We have used the 18O-induced perturbation to the 31P chemical shift to ascertain whether solvent changes result in alterations to the P-O(R) bond. We have studied 16O18O-labeled methyl, ethyl, phenyl, p-nitrophenyl, diethyl p-nitrophenyl, triphenyl, and di-tert-butyl ethyl phosphate in the solvents water, methanol, chloroform, acetonitrile, dioxane, and DMSO. The results suggest no significant solvent-induced weakening of the phosphate ester bonds in any of the solvents tested, and this is unlikely to be a significant source for the acceleration of hydrolysis in mixed solvents.     

π-Stacking interactions at the service of [Cu]-bis(oxazoline) recycling

Anthracene- and pyrene-tagged bis(oxazoline) ligands have been prepared and immobilized on charcoal, fullerene, and single-walled carbon nanotubes through π–π interactions. The corresponding copper complexes have been evaluated for their propensity to promote heterogeneous asymmetric Henry and ene reactions. The best results, in terms of activity, selectivity, and stability toward the recycling procedure have been obtained with the pyrene/SWCNT system, as the first example demonstrating the usefulness of such reversible interactions for the asymmetric formation of new C–C bonds.     

Modeling effects of oxyanion hole on the ester hydrolysis catalyzed by human cholinesterases

Molecular dynamics (MD) simulations and hydrogen bonding energy (HBE) calculations have been performed on the prereactive enzyme-substrate complexes (ES), transition states (TS1), and intermediates (INT1) for acetylcholinesterase (AChE)-catalyzed hydrolysis of acetylcholine (ACh), butyrylcholinesterase (BChE)-catalyzed hydrolysis of ACh, and BChE-catalyzed hydrolysis of (+)/(-)-cocaine to examine the protein environmental effects on the catalytic reactions. The hydrogen bonding of cocaine with the oxyanion hole of BChE is found to be remarkably different from that of ACh with AChE/BChE. Whereas G121/G116, G122/G117, and A204/A199 of AChE/BChE all can form hydrogen bonds with ACh to stabilize the transition state during the ACh hydrolysis, BChE only uses G117 and A199 to form hydrogen bonds with cocaine. The change of the estimated total HBE from ES to TS1 is ca. -5.4/-4.4 kcal/mol for AChE/BChE-catalyzed hydrolysis of ACh and ca. -1.7/-0.8 kcal/mol for BChE-catalyzed hydrolysis of (+)/(-)-cocaine. The remarkable difference of approximately 3 to 5 kcal/mol reveals that the oxyanion hole of AChE/BChE can lower the energy barrier of the ACh hydrolysis significantly more than that of BChE for the cocaine hydrolysis. These results help to understand why the catalytic activity of AChE against ACh is considerably higher than that of BChE against cocaine and provides valuable clues on how to improve the catalytic activity of BChE against cocaine.     

Preparation of an aluminum oxo-hydroxide gel in organic medium

A new method has been developed to prepare aluminum oxohydroxide containing spinnable material and gel. Partial hydrolysis of Al(NO₃)₃·9H₂O in 1-propanol at 78°C produces a spinnable, viscous mixture. The role of the propanol in the hydrolysis proved to be to decrease the polarity of the solvent. In this medium the dissociation of nitric acid is driven back and it decomposes to nitrous gases resulting in the increase of pH in the solution. The conditions have been optimized to obtain the highest hydrolysis degree and to avoid precipitation of basic aluminum nitrate. The resulting optimal temperature is 76–80°C, the time needed is at least 15 h in the case of a laboratory scale preparation. Increasing the ratio of propanol: water and the concentration of Al(III) to the maximum value, leads to the decomposition of 54% of the initial amount NO ₃ ^– ion. By careful drying, the decomposition continues to about 70% and a solid foam comes into existence from the viscous mixture. This foam is able to swell in water, the degree of swelling in mass is about 10. The drying of swollen gel was examined. The spinnable mixture most likely contains polymer chains built up by H-bonds, the foam and the gel probably contain platelets.     

Primary structure of subunit B of the 11S globulin of cotton seeds of variety 108-F. IV. High-molecular-weight peptides from the complete tryptic hydrolysis and from tryptic hydrolysis at the arginine residues of subunit B

The high-molecular-weight peptides from the complete tryptic hydrolysis and tryptic hydrolysis at arginine residues of subunit B, which contained uncleaved bonds of the basic amino acids, have been studied. In the investigation of these peptides, use was made of additional cleavage by trypsin at lysine residues and of cyanogen bromide cleavage.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 227–230, March–April, 1984.     

Acid-catalyzed methanolysis of tri-O-methylamylose and tri-O-methylcellulose

Past experimental evidence has indicated that the acid-catalyzed hydrolysis of polysaccharides does not proceed randomly, and it has been suggested that hydrolysis is more rapid for the glycosidic bonds by which the nonreducing endgroups are attached. To test this hypothesis, amylose and cellulose were permethylated and subjected to methanolysis. It was found that in both the methanolysis of tri-O-methylamylose and tri-O-methylcellulose the production of methyl 2,3,4,6-tetra-O-methyl-α,β-D -glucopyranoside was complete before the production of methyl 2,3,6-tri-O-methyl-α,β-D -glucoside was finished. Since the former compound could only come from the original nonreducing end units and the latter from all other units, these results were interpreted as giving support to the idea of a preferential scission of the bonds at the nonreducing ends, even though the release of original end units was not complete until 70–85% of the glycosidic bonds had been cleaved. It was concluded that methanolysis proceeds by a modification of the hydrolysis mechanism and that methanolysis is therefore a poor model for hydrolysis.     

Functional composition and IR spectra of cottonseed husk hydrolysis lignin and its derivatives

The functional compositions of cottonseed husk hydrolysis lignin and its derivatives have been determined and their IR spectra have been studied. A possible formation of stronger hydrogen bonds in derivatives of hydrolysis lignin has been shown.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Republic of Uzbekistan, Tashkent, fax (3712) 40 64 75. Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 392–397, May–June, 1999.     

Process Evaluation of Enzymatic Hydrolysis with Filtrate Recycle for the Production of High Concentration Sugars

Process simulation and lab trials were carried out to demonstrate and confirm the efficiency of the concept that recycling hydrolysate at low total solid enzymatic hydrolysis is one of the options to increase the sugar concentration without mixing problems. Higher sugar concentration can reduce the capital cost for fermentation and distillation because of smaller retention volume. Meanwhile, operation cost will also decrease for less operating volume and less energy required for distillation. With the computer simulation, time and efforts can be saved to achieve the steady state of recycling process, which is the scenario for industrial production. This paper, to the best of our knowledge, is the first paper discussing steady-state saccharification with recycling of the filtrate form enzymatic hydrolysis to increase sugar concentration. Recycled enzymes in the filtrate (15–30% of the original enzyme loading) resulted in 5–10% higher carbohydrate conversion compared to the case in which recycled enzymes were denatured. The recycled hydrolysate yielded 10% higher carbohydrate conversion compared to pure sugar simulated hydrolysate at the same enzyme loading, which indicated hydrolysis by-products could boost enzymatic hydrolysis. The high sugar concentration (pure sugar simulated) showed inhibition effect, since about 15% decrease in carbohydrate conversion was observed compared with the case with no sugar added. The overall effect of hydrolysate recycling at WinGEMS simulated steady-state conditions with 5% total solids was increasing the sugar concentration from 35 to 141 g/l, while the carbohydrate conversion was 2% higher for recycling at steady state (87%) compared with no recycling strategy (85%). Ten percent and 15% total solid processes were also evaluated in this study.     

聚醚聚氨酯的光聚合及其产物的性能

感光材料;扩链剂;聚醚聚氨酯的光聚合及其产物的性能     

Rationalizing perhydrolase activity of aryl-esterase and subtilisin Carlsberg mutants by molecular dynamics simulations of the second tetrahedral intermediate state

The perhydrolysis reaction in hydrolases is an important example of catalytic promiscuity and has many potential industrial applications. The mechanisms of perhydrolase activity of a subtilisin Carlsberg mutant and of an aryl-esterase mutant have been investigated using classical molecular dynamics simulations of the second tetrahedral intermediate (TI) state. The simulations demonstrated that hydrogen bonding between the second TI of the perhydrolysis reaction is possible in the mutants but not wild type. The stabilization by hydrogen bonds was specific for the perhydrolysis intermediate and either no hydrogen bonding or only weakened hydrogen bonding to the second TI state of the hydrolysis reaction was observed. Furthermore, a significant hindrance to the formation of the catalytically important hydrogen bond between His64 and Ser221 in the catalytic triad by competing hydrogen bonds was found for the subtilisin mutant but not wild type enzyme in case of the hydrolysis intermediate. The opposite was observed in case of the perhydrolysis intermediate. The result offers a qualitative explanation for the overall reduced hydrolysis activity of the subtilisin mutant. In addition, the simulations also explain qualitatively the perhydrolysis activity of the enzyme variants and may be helpful for designing enzyme mutants with further improved perhydrolysis activity.     

Selective Alkaline Protease Catalyzed Hydrolysis of Peptide Esters

Procedures for preparing C-terminal free peptides from hydrolysis of its corresponding methyl or benzyl esters catalyzed by alkaline protease has been developed. N-protected peptides having side-chain ester protecting groups or successive hydrophobic amino acid residues in its sequence are hydrolyzed selectively at C-terminal only and leave other bonds (β and γ- ester or peptide bonds) intact. Compounds which cause a side reaction in base mediated saponification could be hydrolyzed safely by this procedure. Products of this hydrolysis are useful intermediates for fragments coupling in the solid phase peptide synthesis.